isAnyTokenRef function
Returns true if the value is a token reference.
Detects both class-based token references (any Prop carrying a TokenSource) and extension type token references registered via DoubleRef.token.
Implementation
bool isAnyTokenRef(Object? value) {
if (value == null) return false;
if (value is Prop) return value.hasToken;
return _doubleTokenRegistry.containsKey(value);
}